U.S. patent application number 11/909260 was filed with the patent office on 2011-05-19 for optical low-pass filter.
Invention is credited to Naoki Kubo, Masaaki Nose, Yoshiharu Tanaka, Ichiro Tsujimura.
Application Number | 20110116162 11/909260 |
Document ID | / |
Family ID | 38287612 |
Filed Date | 2011-05-19 |
United States Patent
Application |
20110116162 |
Kind Code |
A1 |
Tsujimura; Ichiro ; et
al. |
May 19, 2011 |
Optical Low-Pass Filter
Abstract
On the light-entering surface side of a base material 10, a
coating layer 11 in which a high-refractive layer and a
low-refractive layer are sequentially disposed alternately on one
on the other is provided for blocking infrared radiation. One of
the high-refractive layers is configured by an ITO film 11a so that
the conductivity is increased on the surface of the coating layer.
Herein, in view of preventing, to a further extent, the attachment
of dirt and dust by providing the conductivity to the surface of
the coating layer, it is desirable if the outermost high-refractive
layer is made of a transparent conductive material. Moreover, it is
desirable if the total layer thickness is 140 nm or smaller for the
refractive layers formed outside of the high-refractive layer made
of the transparent conductive material.
Inventors: |
Tsujimura; Ichiro; (Osaka,
JP) ; Nose; Masaaki; (Osaka, JP) ; Tanaka;
Yoshiharu; (Osaka, JP) ; Kubo; Naoki; (Hyogo,
JP) |
Family ID: |
38287612 |
Appl. No.: |
11/909260 |
Filed: |
January 17, 2007 |
PCT Filed: |
January 17, 2007 |
PCT NO: |
PCT/JP2007/050594 |
371 Date: |
December 16, 2008 |
Current U.S.
Class: |
359/359 ;
359/507 |
Current CPC
Class: |
H04N 5/232933 20180801;
G02B 27/0006 20130101; G02B 1/11 20130101; H04N 5/23212 20130101;
G02B 27/46 20130101; H04N 5/232122 20180801; G03B 19/12 20130101;
H04N 5/22521 20180801 |
Class at
Publication: |
359/359 ;
359/507 |
International
Class: |
G02B 5/28 20060101
G02B005/28 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 23, 2006 |
JP |
2006-013666 |
Claims
1. An optical low-pass filter, characterized by comprising: a base
material; and a coating layer formed to the base material on a
light-entering surface side, wherein the coating layer includes a
high-refractive layer and a low-refractive layer sequentially
disposed alternately on one on the other for reflecting or passing
through a light of a specific wavelength range, and at least one of
the high-refractive layers is made of a transparent conductive
material, and attachment of dirt and dust to a surface of the
coating layer is prevented.
2. The optical low-pass filter according to claim 1, wherein the
coating layer blocks infrared radiation.
3. The optical low-pass filter according to claim 1 or 2, wherein a
total layer thickness is 140 nm or smaller for the refractive
layers formed outside of the high-refractive layer made of the
transparent conductive material.
4. The optical low-pass filter according to any of claims 1 to 3,
wherein a layer thickness of the high-refractive layer made of the
transparent conductive material is in a range of 200 to 300 nm.
5. The optical low-pass filter according to any of claims 1 to 4,
wherein a layer thickness of the low-refractive layer on a side of
the base material being in contact with the high-refractive layer
made of the transparent conductive material is in a range of 140 to
220 nm.
6. The optical low-pass filter according to any of claims 1 to 5,
wherein the transparent conductive material is a mixture of indium
oxide and tin oxide, and a mixture ratio of the indium oxide is 90
weight percentage or higher.
7. The optical low-pass filter according to any of claims 1 to 6,
wherein the high-refractive layer being outermost is made of the
transparent conductive material.
8. The optical low-pass filter according to any of claims 1 to 7,
wherein the low-refractive layer being outermost is configured as
an equivalent layer at least of two layers of an MgF.sub.2 layer
and an SiO.sub.2 layer, and the MgF.sub.2 layer and the SiO.sub.2
layer are disposed in order from an outside.
9. The optical low-pass filter according to claim 8, wherein a
layer thickness of the MgF.sub.2 layer and that of the SiO.sub.2
layer are each in a range of 20 to 80 nm.
10. An imaging unit, characterized by comprising: the optical
low-pass filter of any of claims 1 to 9, and an imaging device,
wherein the coating layer of the optical low-pass filter is
connected to a ground potential.
11. An imaging device, characterized by comprising the imaging unit
of claim 10.
Description
TECHNICAL FIELD
[0001] The present invention relates to an optical low-pass filter
(hereinafter, sometimes referred to simply as "low-pass filter")
and, more specifically, to an optical low-pass filter provided with
a coating layer effectively working for infrared blocking,
antireflection, and others.
BACKGROUND ART
[0002] In recent years, an imaging apparatus such as still video
camera or video camera is becoming rapidly popular for
electronically storing images. With such an imaging apparatus, the
image of an object formed by a camera lens is converted into an
electric signal for every pixel by an imaging device such as CCD
and CMOS, and the result is stored in a recoding medium as image
data.
[0003] With such an imaging apparatus, because the imaging device
includes regularly-aligned pixels on a light reception surface,
when an object for imaging has any spatial frequency component
approximated to a sampling spatial frequency that is determined by
pixel spacing, moire appears in the image data of the object.
Moreover, because the imaging device has the spectral sensibility
different from that of human eyes and high sensibility not only for
visible radiation but also for infrared radiation, there needs to
remove any infrared radiation from radiation to the object.
Therefore, a low-pass filter and an infrared blocking filter are
generally disposed between a camera lens and an imaging device.
[0004] The issue here is that optical devices such as low-pass
filter and infrared blocking filter are each made of an insulation
material, and thus are easily attached with dirt and dust due to
static buildup easily caused by piezoelectric effects and
pyroelectric effects. There is a problem that, when these optical
devices are attached with dirt and dust, the shadows of the dirt
and dust are possibly captured by the imaging device. With this
being the case, the closer the dirt and dust to the imaging device,
the more focused the dirt and dust will be. Therefore, the dirt and
dust are to be clearly perceived in the captured image. Especially
with a camera such as single-lens reflex camera in which the camera
lens is exchangeable, it is highly possible that the dirt and dust
get into the camera at the time of lens exchange, thereby easily
causing the problem as above.
[0005] In order to prevent the attachment of dirt and dust due to
static buildup, a proposal has been made to form a transparent
conductive film on the surface of the optical device such as
low-pass filter for the aim of removing the static electricity, for
example. However, if the transparent conductive film is a coating
film of metal or others, the light will be reflected on the coating
film of metal because the coating film of metal is high in
refraction index, thereby causing a new problem of reducing the
light amount of the radiation to the object entering the imaging
device.
[0006] In consideration thereof, in Patent Document 1, for example,
proposed is to suppress the reflection on the surface of a low-pass
filter by forming a transparent conductive film on the base surface
of the low-pass filter, and an antireflective film over the
conductive film.
[0007] [Patent Document 1] JP-A-2002-33468
DISCLOSURE OF THE INVENTION
Problems that the Invention is to Solve
[0008] With the technology proposed as such, the surface of the
low-pass filter is indeed protected from attachment of dirt and
dust and light reflection thereon, however, an optical device such
as infrared blocking filter is required to be separately provided
as with the previous technology. This has thus imposed limitations
on size reduction of apparatus. Moreover, the number of components
is large, and thus the productivity has not been high.
[0009] The invention is proposed in consideration of such previous
problems, and an object thereof is to provide an optical low-pass
filter that can effectively prevent attachment of dirt and dust
caused by static buildup without increasing the number of
components and processes for manufacturing.
[0010] Another object of the invention is to provide an imaging
unit and an imaging device with which the number of components is
small, the manufacturing productivity is high, the size reduction
is possible, and the high image quality can be derived.
Means for Solving the Problems
[0011] In order to achieve the above-described objects, an optical
low-pass filter of the invention is provided with a base material,
and a coating layer formed to the base material on the
light-entering surface side. The coating layer includes a
high-refractive layer and a low-refractive layer sequentially
disposed alternately on one on the other for reflecting or passing
through a light of a specific wavelength range, and at least one of
the high-refractive layers is made of a transparent conductive
material so that the attachment of dirt and dust to the surface of
the coating layer is prevented.
[0012] Herein, the coating layer may be the one that blocks
infrared radiation.
[0013] Moreover, in view of suppressing, to a further extent, the
attachment of dirt and dust by providing the conductivity to the
surface of the coating layer, it is preferable if the outermost
high-refractive layer is made of a transparent conductive material.
Furthermore, a total layer thickness is desirably 140 nm or smaller
for the refractive layers formed outside of the high-refractive
layer made of the transparent conductive material.
[0014] Still further, in view of suppressing the light reflex loss
on the high-refractive layer made of the transparent conductive
material while keeping the conductivity of the surface of the
coating layer, the layer thickness of the high-refractive layer is
preferably in the range of 200 to 300 nm.
[0015] Still further, in view of suppressing the light reflex loss
in the visible light region by the coating layer, the layer
thickness of the low-refractive layer on the base material side
being in contact with the high-refractive layer made of the
transparent conductive material is preferably in the range of 140
to 220 nm.
[0016] Still further, in view of suppressing the light absorption,
preferably, the transparent conductive material is a mixture of
indium oxide and tin oxide, and a mixture ratio of the indium oxide
is 90 weight percentage or higher.
[0017] Preferably, the outermost low-refractive layer is configured
as an equivalent layer at least of two layers of MgF.sub.2 layer
and SiO.sub.2 layer, and the MgF.sub.2 layer and the SiO.sub.2
layer are disposed in order from the outside. Herein, preferably,
the layer thickness of the MgF.sub.2 layer and that of the
SiO.sub.2 layer are each in the range of 20 to 80 nm.
[0018] An imaging unit according to the invention of achieving the
above-described objects is characterized by including any one of
the above-described optical low-pass filters, and an imaging
device, and in the imaging unit, the coating layer of the optical
low-pass filter is connected to a ground potential.
[0019] Further, an imaging device of the invention is characterized
by including the imaging unit.
Advantage of the Invention
[0020] With the optical low-pass filter of the invention, a light
of a specific wavelength range is reflected or passed through. A
coating layer in which a high-refractive layer and a low-refractive
layer are sequentially disposed alternately on one on the other is
formed on the surface of the base material, and at least one of the
high-refractive layers of the coating layer is made of a
transparent conductive material. The configuration can thus
achieve, all at once, the coating of reflecting or passing through
the light of a specific wavelength range, and the ensuring of the
conductivity on the surface of the low-pass filter. This eliminates
the need to provide a conductive member separately from a coating
member of reflecting or passing through a light of a specific
wavelength range, thereby being able to effectively prevent the
attachment of dirt and dust to the surface of the low-pass filter
while suppressing the cost.
[0021] Moreover, if the outermost high-refractive layer is made of
a transparent conductive material, the attachment of dirt and dust
can be prevented to a further extent. Further, when the total layer
thickness is 140 nm or smaller for the refractive layers formed
outside of the high-refractive layer made of the transparent
conductive material, the coating layer can have the satisfactory
conductivity on the surface, and a simple grounding configuration
allows grounding so that the attachment of dirt and dust can be
prevented to a further degree.
[0022] Further, if the layer thickness is in the range of 200 to
300 nm for the high-refractive layer made of the transparent
conductive material, the light reflex loss can be suppressed on the
coating layer while the conductivity is being retained on the
surface of the coating layer.
[0023] When the layer thickness is in the range of 140 to 220 nm
for the low-refractive layer on the base material side being in
contact with the high-refractive layer made of the transparent
conductive material, the light reflex loss can be suppressed in the
visible light region by the coating layer.
[0024] When the transparent conductive material is a mixture of
indium oxide and tin oxide with a mixture ratio of the indium oxide
being 90 weight percentage or higher, the light absorption can be
suppressed.
[0025] When the outermost low-refractive layer is configured as an
equivalent layer at least of two layers of MgF.sub.2 layer and
SiO.sub.2 layer, and when the MgF.sub.2 layer and the SiO.sub.2
layer are disposed in order from the outside, the result will show
excellent solvent-resistance and environment-resistance while
suppressing the attachment of dirt and dust. This serves more
effects when the layer thickness of the MgF.sub.2 layer and that of
the SiO.sub.2 layer each fall in the range of 20 to 80 nm.
[0026] With the imaging unit and the imaging device of the
invention, the optical low-pass filter is any of those described
above, and thus the previously-provided optical device that
reflects or passes through a light of a specific wavelength range
can be eliminated so that the productivity can be increased, and
the apparatus can be reduced in size. Moreover, because the surface
of the optical low-pass filter can be protected from attachment of
dirt and dust, the resulting captured image can be high in image
quality.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a schematic diagram showing an exemplary low-pass
filter of the invention.
[0028] FIG. 2 is a schematic diagram showing another exemplary
low-pass filter of the invention.
[0029] FIG. 3 is a schematic diagram showing still another
exemplary low-pass filter of the invention.
[0030] FIG. 4 is a graph showing the transmittance when a
low-refractive layer directly beneath an ITO film is changed in
layer thickness.
[0031] FIG. 5A is a graph showing the light absorption when the
mixture ratio is changed between indium oxide and tin oxide.
[0032] FIG. 5B is a graph showing the light absorption when the
mixture ratio is changed between indium oxide and tin oxide.
[0033] FIG. 6A is a graph showing the light transmittance when the
mixture ratio is changed between indium oxide and tin oxide.
[0034] FIG. 6B is a graph showing the transmittance when the
mixture ratio is changed between indium oxide and tin oxide.
[0035] FIG. 7 is a schematic diagram showing an exemplary imaging
unit of the invention.
[0036] FIG. 8A is a front view of an exemplary camera (imaging
device) of the invention.
[0037] FIG. 8B is a rear view of the exemplary camera (imaging
device) of the invention.
[0038] FIG. 9A is a diagram showing the internal configuration of
the camera of FIGS. 8A and 8B.
[0039] FIG. 9B is a diagram showing the internal configuration of
the camera of FIGS. 8A and 8B.
[0040] FIG. 10 is a control block diagram of the camera of FIGS. 8A
and 8B.
BEST MODE FOR CARRYING OUT THE INVENTION
[0041] In the below, an embodiment of the invention is described by
referring to the accompanying drawings. Note here that the
invention is not at all restrictive to such an embodiment.
[0042] FIG. 1 is a schematic diagram showing an embodiment of a
low-pass filter in the invention. A low-pass filter 1 in the
drawing includes a coating layer 11 of blocking infrared radiation
formed on the surface of a base material 10. The coating layer 11
of blocking the infrared radiation includes a high-refractive layer
and a low-refractive layer sequentially disposed alternately on one
on the other. One of the high-refractive layers is configured by an
ITO (Indium Tin Oxide) film 11a made of a mixture of indium oxide
and tin oxide being a transparent conductive material. With such a
configuration, the surface of the coating layer is increased in
conductivity, and the attachment of dirt and dust due to static
buildup can be effectively prevented.
[0043] Among the high-refractive layers configuring the coating
layer 11, there is no specific restriction on which high-refractive
layer is to be made of a conductive material, but the closer to the
surface of the coating layer, the more the effects thereof, and the
further from the surface of the coating surface, the less the
effects thereof. As such, it is recommended to form the outermost
high-refractive layer using a transparent conductive material. Note
that the outermost layer of the coating layer 11 is generally a
low-refractive layer, and thus the outermost high-refractive layer
is generally the second layer from the outside.
[0044] As shown in FIG. 2, any of the high-refractive layers other
than the outermost high-refractive layer may be made of the
transparent conductive material. If this is the case, desirably,
the total layer thickness D is 140 nm or smaller for the refractive
layers formed outside of the high-refractive layer made of the
transparent conductive material. When the total layer thickness D
exceeds 140 nm, there is a possibility that the surface of the
coating layer will not have sufficiently-high conductivity, whereby
the effects of preventing the attachment of dirt and dust may not
serve well enough.
[0045] Moreover, there is no specific restriction on the layer
thickness for the high-refractive layer made of the transparent
conductive material, and may be determined as appropriate based on
the specific material used for the transparent conductive material,
the position of forming the layer made of the transparent
conductive material, and others. The range of 200 to 300 nm is
generally desirable. When the layer thickness of the
high-refractive layer made of the transparent conductive material
is thinner than 200 nm, there is a possibility that the surface of
the coating layer is not provided with sufficient conductivity. On
the other hand, when the layer thickness exceeds 300 nm, there is a
possibility that the light absorption occurs in the high-refractive
layer. The more-preferable layer thickness is in the range of 210
to 260 nm.
[0046] The outermost layer of the coating layer is generally a
low-refractive layer as described above. This outermost layer is a
layer directly attached with dirt and dust, and it is thus
desirable to be made of a material hardly causing, physically, dirt
and dust attachment. For the material being non-sticky with low
refraction index, a fluorine compound, especially MgF.sub.2 is
considered suitable. In consideration thereof, the inventor et al.
of the invention has conducted an experiment using MgF.sub.2 for
the outermost layer of the coating layer. The experiment result is
shown in Table 1. Note that, in this experiment, an ITO film is
formed on the surface of a soda-lime glass, and a low-refractive
layer is formed thereon to go through the following solvent test
and reliability test, and to evaluate the performance of dirt and
dust falling-off.
[0047] (Solvent Test)
[0048] [EE3310] (washing solvent manufactured by Olympus Imaging
Corp.), using a lens-cleaning paper soaked with a solvent of
ethanol and another soaked with a solvent of IPA (isopropyl
alcohol), samples are each wiped for 50 reciprocating motions with
the weighing of 200 g, and then the surfaces of the samples are
evaluated by visual observations. The evaluation criteria are as
below. [.largecircle.]: good, [.DELTA.]: slight problem is observed
but practically no problem, [.times.]: practical problem is
observed
[0049] (Reliability Test)
[0050] In a thermal shock test, a sample is put under, alternately
for an hour, the environment of -30 degrees and that of +70
degrees, and this is repeated for 10 cycles. Thereafter, the
surface of the sample is evaluated by visual observations.
[0051] In a temperature/humidity test, a sample is left for 500
hours under the environment of each temperature and humidity, and
then for 24 hours under the room temperature and the room humidity.
Thereafter, the surface of the sample is evaluated by visual
observations.
[0052] The evaluation criteria are the same as those for the
solvent test.
[0053] (Performance of Dirt and Dust Falling-Off)
[0054] Powders of alumina or others are scattered on the surface of
a low-pass filter, and the low-pass filter is vibrated by a
predetermined amount for a predetermined length of time.
Thereafter, the remaining amount of powders on the surface of the
low-pass filter is evaluated by visual observations. The evaluation
criteria are as below. [.largecircle.]: almost gone, [.DELTA.]:
remains with the level of no influence on image, [.times.]: remains
with the level of influence on image
TABLE-US-00001 TABLE 1 Reliability Test Performance of Experiment
ITO SiO.sub.2 MgF.sub.2 Solvent Test thermal 70.degree. C./ Dirt
and Dust No. (nm) (nm) (nm) EE3310 Ethanol IPA shock test
35.degree. C./85% 60.degree. C./90% 70.degree. C./80% no humidity
Falling-Off 1 240 90 0 .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .DELTA. 2 240 0 90 .DELTA. fog .DELTA. fog .DELTA.
fog .largecircle. .largecircle. .largecircle. .DELTA. fog
.largecircle. .largecircle. 3 240 47 47 .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. 4 240 22 72 .DELTA. fog
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle. 5 240 66 20
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle. .DELTA. 6 0
0 90 .largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle. X 7 0 47 47
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle. X 8 0 22 72
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle. X 9 0 66 20
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle. X Layer
Configuration of Sample MgF.sub.2 SiO.sub.2 ITO Film Glass
[0055] In Table 1, with the sample of Experiment No. 1 in which the
outermost layer is an SiO.sub.2 layer being a low-refractive layer,
the solvent test and the reliability test show good results, but a
slight problem is observed for the performance of dirt and dust
falling-off. On the other hand, with the sample of Experiment No. 2
in which the outermost layer is an MgF.sub.2 layer being a
low-refractive layer, the performance of dirt and dust falling-off
shows good result but "fog" is observed in the solvent test. Note
that, with the samples of Experiment Nos. 6 to 9 formed with no ITO
film, all show a practical problem for the performance of dirt and
dust falling-off.
[0056] In consideration thereof, the inventor et al. of the
invention has come up with an idea that a low-refractive layer
being the outermost layer of the coating layer may be configured as
an equivalent layer at least of two layers of MgF.sub.2 layer and
SiO.sub.2 layer, and if so, the disadvantages of these two layers
may be complemented each other. The samples 3 to 5 are thus
manufactured for evaluation. Herein, the layers are disposed one on
the other in order of ITO film, SiO.sub.2 layer, and MgF.sub.2
layer. As a result, assuming that the outermost layer of the
coating layer is an equivalent layer of two layers of MgF.sub.2
layer and SiO.sub.2 layer, the solvent test, the reliability test,
and the performance of dirt and dust falling-off are found out as
all showing the excellent results. For the MgF.sub.2 layer and the
SiO.sub.2 layer formed as an outermost layer of the coating layer,
the layer thickness is preferably in the range of 20 to 80 nm, and
the more preferable lower bound value is 30 nm.
[0057] Moreover, a layer thickness d (shown in FIG. 3) of the
low-refractive layer located below the high-refractive layer made
of a transparent conductive material is preferably in the range of
140 to 220 nm. With the sample of the layer configuration of FIG.
3, the layer thickness d is changed to 92, 178, and 266 nm, and the
transmittance of the sample is simulated. The experiment result is
shown in FIG. 4.
[0058] As is evident from the drawing, when the layer thickness d
of the low-refractive layer is 178 nm, the transmittance of the
wavelength in the visible light region is substantially 100%. On
the other hand, when the layer thickness d is 92 nm and 266 nm, the
transmittance of the wavelength in the visible light region is 80
to 95%, and the light reflex loss is observed in the coating
layer.
[0059] The transparent conductive material for use in the invention
can be of any previously well-known, and includes antimony oxide,
indium oxide, tin oxide, zinc oxide, ITO (Tin-doped Indium Oxide),
ATO (Antimony-doped Tin Oxide), and others. Among these, ITO is
preferable.
[0060] The inventor et al. of the invention also gives careful
consideration to the mixture ratio of the indium oxide and tin
oxide in the ITO. The experiment results derived by changing the
mixture ratio of indium oxide (InO.sub.3) and the tin oxide
(SnO.sub.2) are shown in FIGS. 5A, 5B, 6A, and 6B. FIGS. 5A and 5B
are each a graph showing the amount of light absorption for every
wavelength with the lateral axis of wavelength (nm), and the
vertical axis of light absorption (%). FIGS. 6A and 6B are each a
graph showing the transmittance for every wavelength with the
lateral axis of wavelength (nm) and the vertical axis of
transmittance (%).
[0061] FIG. 5A is a graph showing the amount of light absorption in
an ITO film with InO.sub.3:SnO.sub.2 being 86:14 by weight ratio,
and InO.sub.3:SnO.sub.2 is 95:5 thereby in FIG. 5B. Through
comparison of these graphs, it is known that the light absorption
in the visible light region is smaller in the ITO film with
InO.sub.3:SnO.sub.2 being 95:5. FIG. 6A is a graph showing the
transmittance of an ITO film with InO.sub.3:SnO.sub.2 being 86:14
by weight ratio, and InO.sub.3:SnO.sub.2 is 95:5 thereby in FIG.
6B. Through comparison of these graphs, it is known that the
transmittance in the visible light region is better in the ITO film
with InO.sub.3:SnO.sub.2 being 95:5. These experiment results tell
that, as a transparent conductive material for use in the
invention, the ITO in which the mixture ratio of indium oxide is 90
weight percent or more is preferable.
[0062] The material for use as a base material of a low-pass filter
is exemplified by quartz, lithium niobate, vanadium tetraoxide, and
others. As to the layer configuration of the coating layer, a
high-refractive layer and a low-refractive layer may be alternately
disposed on one on the other, and it may be so formed as to work to
derive any expected effects such as working for infrared blocking
and antireflection. If with a coating layer provided for the aim of
infrared blocking, for example, the total number of layers will be
about 30 to 40. The material for a high-refractive layer in the
coating layer is preferably at least one of titanium oxide,
tantalum oxide, a mixture of titanium oxide and lanthanum oxide,
and a mixture of titanium oxide and tantalum oxide. The material
for a low-refractive layer is preferably at least one of silicon
oxide, aluminum oxide, and a mixture of silicon oxide and aluminum
oxide.
[0063] The forming method of the coating layer is not specifically
restrictive, and any previously-known method can be used, e.g.,
vacuum deposition, IAD (Ion Assist Deposition), IP (Ion Plating),
CVD (Chemical Vapor Deposition), sputtering, and others.
[0064] In view of suppressing the physical absorption of dirt and
dust, the coating layer may be surely coated thereon also with
fluorine. With this being the case, the film thickness of the
fluorine coating film is required to be in the range not
influencing the optical characteristics. Specifically, about a few
nm is considered preferable.
[0065] FIG. 7 shows a schematic diagram of an imaging unit 2 using
the optical low-pass filter 1 of the invention. The imaging unit 2
of FIG. 7 is provided with: a box-shaped housing 22 formed with an
aperture on the front and rear surfaces; a leaf spring 26 attached,
with a substantially "S"-shaped cross section, to the outer edge
portion of the aperture on the front surface to protrude inward of
the aperture; the low-pass filter 1 attached as if abutting the
inner surface of the leaf spring 26 via a mask sheet 25; a CCD
(Charge Coupled Device) 21 being an imaging device attached to
oppose the low-pass filter 1 with a space therefrom via a spacer
27, a radiator plate 23 attached to seal the aperture on the rear
surface of the housing 22; and a substrate 24 attached to the rear
surface of the radiator plate 23. Into a screw hole punched in the
end surface of the housing 22 on the rear surface side, in the
state that a through hole formed to the radiator plate 23 is
aligned with that formed to the substrate 24, a screw 28 is screwed
together the screw hole after going through the through holes from
the outside so that the components are combined together as a
piece. On the surface of the base material 10 of the low-pass
filter 1, the infrared blocking coating layer 11 is formed, and as
shown in FIG. 3, a high-refractive layer located outermost in the
infrared blocking coating layer 11 is formed by the ITO film 11a.
The infrared blocking coating layer 11 is connected to the ground
potential via the mask sheet 25, the leaf spring 26, the hosing 22,
and the substrate 24.
[0066] With the imaging unit 2 of such a configuration, although
any special configuration has been required to keep the
conductivity, the simple configuration enables to keep the
conductivity and an infrared blocking filter, and the number of
components can be reduced. Moreover, this also enables size
reduction of the apparatus.
[0067] The CCD 21 used herein is configured by a so-called one-chip
color area sensor of so-called Bayer type, in which the surfaces of
CCDs in the two-dimensionally-disposed area sensor are attached
with color filters of R (red), G (green), and B (blue) in a
checkered pattern. In this embodiment, it has 3008 (X
direction).times.2000 (Y direction)=6016000 pixels, for
example.
[0068] Note that the imaging device for use in the invention is not
restrictive to the CCD, and any other previously-known devices such
as CMOS and VMIS can be used.
[0069] FIGS. 8A and 8B show an exemplary still video camera
equipped with the optical low-pass filter and the imaging unit of
the invention. FIG. 8A is a front view of the still video camera of
the invention, and FIG. 8B is a rear view thereof.
[0070] The still video camera of FIGS. 8A and 8B is a
single-lens-reflex still video camera provided with a camera body
4, and an interchangeable lens 3 being attachable/removable to/from
at the substantial center on the front surface of the camera body
4. The camera body 4 is provided with: a mount section (not shown)
for attachment of the interchangeable lens 3 at substantially the
center on the front surface; a lens exchange button 41 for
attaching/removing the interchangeable lens to/from the area in the
vicinity of the mount section; a grip section 42 for a user to hold
at the left end portion on the front surface; an illumination
window 46 from which a light exits for use to measure the distance
from an object; a control value setting dial 43 for use to set a
control value at the upper right portion on the front surface; a
mode setting dial 44 for use to switch a shooting mode at the upper
left portion on the front surface; a release button 45 for use to
issue a command of starting/ending exposure on the upper surface of
the grip section 42; and an AF mode setting dial 47 for use to
switch an auto focus mode at the lower right portion on the front
surface. In the vicinity of the mount section, provided are a
plurality of electrical contact points (not shown) for establishing
an electric connection with the attached interchangeable lens 3,
and a plurality of couplers (not shown) for establishing a
mechanical connection.
[0071] The electrical contact points are provided for sending out,
from a lens ROM (Read Only Memory) equipped in the interchangeable
lens 3 to a control section inside of the camera body 4 (refer to
FIG. 10), information unique to the lens (information about
aperture F value, focus distance, and others), or for sending out,
to the control section, information about the position of a focus
lens in the interchangeable lane 3 or position of a zoom lens
therein, for example.
[0072] The couplers are provide for transmitting, to the lenses in
the interchangeable lens 3, the driving force of a focus lens
driving motor equipped in the camera body 4, and the driving force
of a zoom lens driving motor equipped therein.
[0073] The mode setting dial 44 is provided for setting a plurality
of shooting modes including a still image shooting mode for
shooting still images, and a moving image shooting mode for
shooting moving images.
[0074] The release button 45 is so configured as to be operated
with "half depression state" in which the button is half-depressed,
and with "full depression state" in which the button is further
depressed. In the still image shooting mode, when the release
button 45 is half depressed, the preparation operation (preparation
operation for setting of exposure control value, or for focus
adjustment) is executed for shooting of still images of an object.
When the release button 45 is fully depressed, the shooting
operation (a series of operation of exposing a color imaging device
that will be described later, and applying predetermined image
processing to an image signal being a result of the exposure for
storage into a memory card) is executed. In the moving image
shooting mode, when the release button 45 is fully depressed, the
shooting operation (a series of operation of exposing a color
imaging device, and applying predetermined image processing to an
image signal being a result of the exposure for storage into a
memory card) is started, and when the release button 45 is fully
depressed again, the shooting operation is ended.
[0075] In FIG. 8B, at the substantially upper center of the rear
surface of the camera body 4, a finder window 51 is provided. To
the finder window 51, the image of an object is guided from the
interchangeable lens 3. The person who is in charge of imaging
looks into the finder window 51 so that he or she can perceive the
object. At substantially the center of the rear surface of the
camera body 4, an external display section (liquid crystal display
section) 52 is provided. In this embodiment, the external display
section 52 is exemplified by a color liquid crystal display device
with 400 (X direction).times.300 (Y direction)=120000 pixels, for
example. It serves to display a menu screen for setting of a mode
about exposure control in a recording mode, a mode about shooting
scenes, shooting requirements, and others, or for reproducing and
displaying any captured image recorded on a memory card in a
reproduction mode, for example.
[0076] On the upper left portion of the external display section
52, a main switch 53 is provided. The main switch 53 is a
two-position slide switch, and when a contact point is set to the
"OFF" position on the left side, the power is turned off, and when
the contact point is set to the "ON" position on the right side,
the power is turned on.
[0077] On the right side of the external display section 52, a jog
dial key 54 is provided. The jog dial key 54 is provided with a
circular operation button, and in this operation button, depression
operations in four directions of up, down, right, and left, and the
depression operations in four directions of upper right, upper
left, lower right, and lower left are respectively detected.
[0078] The jog dial key 54 is of multi-function, and functions as
an operation switch for changing any item selected on a menu screen
displayed on the external display section 52 for setting of
shooting scene, and functions as an operation switch for changing a
frame being a reproduction target selected on an index screen on
which a plurality of thumbnail images are aligned and displayed,
for example. The jog dial key 54 can also serve as a zoom switch
for changing the focus distance of a zoom lens of the
interchangeable lens 3.
[0079] On the right side of the external display section 52, a
camera shake correction switch 56 is provided. When the camera
shake correction switch 56 is turned on, the camera shake
correction function is activated. At the lower position of the
external display section 52, as a switch for operation execution
about display making or display details on the external display
section 52, various types of switches 55 are provided.
[0080] Described next is the internal configuration of a still
video camera of the invention. FIGS. 9A and 9B show the internal
configuration of a still video camera of the invention. FIG. 9A is
a side cross sectional view of the still video camera, showing the
internal configuration in a shooting wait state, and FIG. 9B is a
side cross sectional view of the still video camera, showing the
internal configuration in a shooting (exposure) state.
[0081] As shown in FIGS. 9A and 9B, a luminous flux of the object
after passing through a camera lens 31 of the interchangeable lens
3 is divided into two, i.e., a reflected luminous flux and a
passing-through luminous flux, by a quick return mirror 61. The
reflected luminous flux is image-formed on a reticle 62 for use for
finder observation, and the resulting formed image of the object is
observed from a finder eyepiece window 65 via a pentaprism 63 and a
eyepiece lens 64. On the other hand, the passing-through luminous
flux is, for use for auto focusing, reflected by a submirror 66
provided on the rear surface of the quick return mirror 61, and
then is guided to a focus detection sensor 67. The focus detection
sensor 67 detects focus information of the object. Behind the quick
return mirror 61, the imaging unit 2 equipped therein the CCD 21
shown in FIG. 7 is attached via a shutter 68. The shutter 68 is so
controlled as to open and close at the time of exposure. Note here
that the shutter 68 is exemplified by a vertical-traveling focal
plane shutter.
[0082] As shown in FIG. 9B, when the release switch 45 (shown in
FIGS. 8A and 8B) of the camera is turned on, the quick return
mirror 61 and the submirror 66 are jumped upward, and stopped in
motion below the reticle 62. Thereafter, when the shutter 68 opens,
the CCD 21 (shown in FIG. 7) is exposed. After exposure, the
shutter 68 is closed, and the quick return mirror 61 and the
submirror 66 return to their original positions.
[0083] FIG. 10 shows the block diagram showing an exemplary
electrical configuration of the still video camera of the
invention. The still video camera is provided with the camera body
4, the interchangeable lens 3, an imaging section 70, a signal
processing section 80, a control section 90, a focus control
section 91, an LCD (display section) 93, an operation section 94,
and others.
[0084] The interchangeable lens 3 is provided with camera lenses
31a and 31b for image-forming of an object onto a CCD 73, a lens
position detection section 320 for detecting the position of the
camera lenses, and a control section 310 for exchanging various
types of information with the control section 90 on the body side,
and exercising control over various types of lenses.
[0085] The various types of lenses equipped in the interchangeable
lens 3 are moved to their predetermined positions by a lens driving
motor M1, which performs driving based on a control signal coming
from the control section 90 via the focus control section 91.
[0086] The imaging section 70 serves to subject the image of an
object coming via the interchangeable lens 3 to photoelectric
conversion, and output the result as an image signal (electric
image). It is provided with: a mirror mechanism 71; a shutter 72;
the CCD (imaging device) 73; a CCD drive mechanism 74; a mirror
control section 75; a shutter control section 76; and a timing
control circuit 77.
[0087] The mirror mechanism 71 includes the quick return mirror 61
(shown in FIGS. 9A and 9B) and the submirror 66 (shown in FIGS. 9A
and 9B), and divides a luminous flux of an object into a luminous
flux for finder observation use and another for auto focusing use.
At the time of imaging of the object, a motor M2 is driven based on
a save signal coming from the mirror control section 75, and the
quick return mirror 61 and the submirror 66 are moved away from the
optical axis of the interchangeable lend 3. When an ON signal of
the release switch 45 (shown in FIGS. 8A and 8B) is input to the
control section 90, this save signal is generated by the control
section 90, and is output to the mirror control section 75.
[0088] The shutter 72 opens and closes when the motor M3 is driven
based on a signal coming from the shutter control section 76.
[0089] Based on a drive control signal (accumulation start
signal/accumulation end signal) provided by the timing control
circuit 77, the CCD 73 receives the image of the object for a
predetermined exposure time for conversion into an image signal
(electric charge accumulation signal), and sends out the image
signal to the signal processing section 80 in accordance with a
reading control signal (e.g., horizontal synchronizing signal,
vertical synchronizing signal, transfer signal) provided by the
timing control circuit 77. At this time, the image signal is
separated into color components or R, G, and B for transmission to
the signal processing section 80.
[0090] The CCD drive mechanism 74 is provided for moving the CCD 73
in such a direction of cancelling the camera shake. The
two-direction camera shake detected by a gyro sensor 97 is
converted by the control section 90 into a camera shake correction
drive signal for transmission to the CCD drive mechanism 74. This
drives the CCD drive mechanism 74.
[0091] Note that, in the below, for convenience of description, for
the aim of distinguishing a reception signal of each of pixels and
an image signal which is a group of the reception signals and
constitutes a captured image, the reception signal of each of the
pixels is referred to as a pixel signal (analog value) or pixel
data (digital value) as required.
[0092] The timing control circuit 77 is provided for controlling
the shooting operation of the CCD 73, and generates a shooting
control signal based on a control signal coming from the control
section 90. This shooting control signal includes a reference clock
signal, a timing signal (synchronous clock signal) for subjecting,
to signal processing in the signal processing section 80, the image
signal provided by the CCD 73, and others. This timing signal is
forwarded to an analog signal processing circuit 81 and an A/D
conversion circuit 82 in the signal processing section 80.
[0093] The signal processing section 80 is provided for subjecting
the image signal coming from the CCD 73 to predetermined analog
signal processing and digital signal processing, and the signal
processing to the image signal is executed for every pixel signal
configuring the image signal. This signal processing section 80 is
provided with: the analog signal processing circuit 81, the A/D
conversion circuit 82, a black level correction circuit 83, a white
balance (WB) circuit 84, a .gamma. correction circuit 85, and an
image memory 86. The black level correction circuit 83, the WB
circuit 84, and the .gamma. correction circuit 85 configure a
circuit for applying the digital signal processing.
[0094] The analog signal processing circuit 81 is provided for
applying predetermined analog signal processing to an image signal
of an analog value coming from the CCD 73, and includes a CDS
(correlated double sampling) circuit of reducing the sampling noise
of the image signal, and an AGC (Auto Gain Control) circuit of
performing level adjustment of the image signal. The AGC circuit
also functions as compensating the not-sufficient level of the
captured image when no appropriate exposure is derived by an f
number provided in the interchangeable lens 3 and the exposure time
of the CCD 73 (e.g., when an image of very low-bright object is
captured). Note that the gain of the AGC circuit is set by the
control section 90.
[0095] The A/D conversion circuit 82 is provided for converting the
image signal coming from the analog signal processing circuit 81
into an image signal of a digital value (hereinafter, referred to
as "image data"), and converts the pixel signal derived through
light reception by each of pixels into 12-bit pixel data, for
example. The black level correction circuit 83 is provided for
correcting the black level of each of the A/D-converted pixel data
to the reference black level.
[0096] The WB circuit 84 is provided for adjusting the white
balance of the captured image, and adjusts the white balance of the
captured image by converting the level of the pixel data for each
of the color components R, G, and B using a level conversion table
provided by the control section 90. Note that the conversion
coefficient for each of the color components of the level
conversion table is set for every captured image by the control
section 90.
[0097] The .gamma. correction circuit 85 is provided for performing
gray scale correction by correcting the .gamma. characteristics of
the pixel data. It includes a plurality types of .gamma. correction
tables varying in .gamma. characteristics as lookup tables (LUTs),
and performs .gamma. correction to the pixel data by any
predetermined .gamma. correction table in accordance with any set
shooting scene. Note that in the .gamma. correction process, the
14-bit pixel data is converted into 8-bit (256 levels of gray
scale) pixel data. The reason why the pixel data before the .gamma.
correction process is 14-bit data is to prevent image degradation
when the .gamma. correction is performed with the high-nonlinearity
.gamma. characteristics. Moreover, the pixel data of each of the
color components R, G, and B is subjected to predetermined level
conversion in the WB circuit 84, and the resulting pixel data is
subjected to .gamma. correction using any corresponding .gamma.
correction table.
[0098] An image memory 86 is a memory for temporarily storing the
image data through with the signal processing, and has the capacity
enough for image data of a plurality of frames. Note that, in this
embodiment, because the CCD 73 has 3002.times.2000=6016000 pixels,
the storage capacity available for image data of a frame is the
capacity available for the 6016000 color pixel data.
[0099] An LCD (display section) 93 is provided with a VRAM 92. The
VRAM 92 is a buffer memory for storing display images to the LCD
93, and has the memory capacity available for 400.times.300 color
pixel data corresponding to the number of the LCD 93.
[0100] The operation section 94 includes a release switch that is
turned on when the release button 45 (shown in FIGS. 8A and 8B) is
fully depressed, the mode setting dial 44 (shown in FIGS. 8A and
8B), and others. Such operation information is forwarded to the
control section 90.
[0101] The control section 90 is a CPU (Central Processing Unit),
for example, and includes a ROM for storing a control program for
control over the operation of the CPU being the control section 90,
and a RAM for temporarily storing various types of data for use in
the computation process or the control process, for example.
[0102] This control section 90 is connected to a memory card 96 via
a card I/F 95. The card I/F 95 is an interface for writing of image
data to the memory card 96 and reading of the image data therefrom.
The memory card 96 records thereon the image data such as still
images and moving images.
[0103] The control section 90 is connected to a communications I/F
101 such as USB terminal. This enables connection to a PC or
others.
[0104] A flash 102 is for illuminating the object at the time of
shooting in any dark place, and light emission is controlled by a
flash circuit 98. A phase-difference AF module 100 is for deriving
an AF signal, and an AF auxiliary light 99 is for deriving the
image of an object for the phase-difference AF module 100 at the
time of shooting in any dark place.
* * * * *